The former head of the U.S. Food and Drug Administration (FDA) Dr. Scott Gottlieb says regulators and public health officials erred in their rollout of the COVID booster vaccine—and that a different approach could have reduced much of the public confusion and skepticism that plagued widespread inoculation.

COVID booster messaging has been inconsistent across federal agencies over the last few months. After the Biden Administration set September 20 as the target date to make boosters available to all U.S. adults, an FDA panel of experts threw a wrench into that ambitious plan a month later, recommending a third dose of the Pfizer vaccine for a more select group, including the elderly and those at high risk of severe disease.

Not long after, a panel of advisers to the Centers for Disease Control (CDC) made its own recommendations before CDC Director Dr. Rochelle Walensky seemed to overrule the panel and approve boosters for an expanded group that included those 18 to 64 years old who live in institutional settings that increase their risk of exposure, such as prisons or homeless shelters, or are employed as health care workers.

While this back-and-forth exchange of differing federal opinions may have made sense in pre-pandemic times, according to Gottlieb, a different approach is required in the midst of a public health crisis.

“We took a peace-time construct and applied it to a wartime setting in a public health emergency, without taking a step back and saying what would be the optimal process,” Gottlieb, who is also a Pfizer board member, told Fortune.

As far as the optimal process goes, Gottlieb—who served as commissioner of the FDA for two years during the Trump Administration—thinks there should have been greater alignment and cooperation between the FDA and the CDC about COVID vaccine decision-making.

In normal times, authorization and approval of a vaccine is intentionally “designed to be a deliberative” and “prolonged” process, according to Gottlieb, who recently authored a book on what he believes went wrong with the nation's response to COVID titled, Uncontrolled Spread. Because pediatric vaccines are most often the shots up for evaluation, regulators and health experts make an effort not to rush the process, instead collecting large amounts of data over an extended period of time to ensure childhood immunizations are safe and effective.

"We took the system that exists for adjudicating what pediatric vaccines should be in the childhood immunization schedule, and we adopted that system for making decisions about the distribution of a vaccine that's being offered on an emergency use basis in the setting of a global public health crisis to adults, who have discretion over whether or not they take the vaccine," he said. "That's a very different exercise."

Plus, in non-pandemic circumstances, Gottlieb said both the FDA commissioner (usually a politically appointed figure) and the CDC director (historically a subject matter expert) get to render a verdict on whether a vaccine should be approved and to what extent. While the FDA usually makes broad approvals for vaccines, according to Gottlieb, the CDC tends to err on the side of caution, generally favoring a more staged rollout of vaccines to specific demographics. These two different approaches to vaccine approval naturally lead to conflict—something Gottlieb said is healthy and necessary in usual times.

“So by virtue of the fact that [the FDA and CDC are] each being asked to render a verdict on the same question, but being asked to look at it through a different prism, you're going to get conflict,” Gottlieb said. “That system is designed to do that, because people, in good wisdom, recognize that when you're making decisions around distributing a vaccine, largely to a pediatric population where you're mandating childhood vaccinations, you want a highly deliberative, careful, thoughtful process with a lots of checks and balances. Because these are weighty decisions.”

But in the setting of a public health crisis, Gottlieb said there is no room for the perception of conflict, as “it's going to be used by people who want to sow confusion and want to sow doubt as a way to inappropriately send a message to consumers that public health officials are discordant and not in agreement.”

Instead, the former FDA head thinks the two agencies should have made an effort to work co-dependently from the very beginning given the extenuating circumstances of a pandemic.

“In an ideal world, I think you would have gotten the FDA and CDC aligned to come up with a unified recommendation,” Gottlieb said. “There's nothing in regulation or law saying that we can't design a hybrid process here.”

Mixing and match vaccines

When asked about the timeline for other boosters of other COVID vaccines, Gottlieb noted that data regarding booster shots for both the Moderna and the Johnson & Johnson vaccines is going to be available very soon. He added that both companies are actively working to adjudicate their applications with the FDA and that data on the Johnson & Johnson booster "looked very good."

In the meantime, though, the National Institutes of Health (NIH) is undertaking a study looking at "mixing and matching and using the different vaccines interchangeably," according to Gottlieb. In other words, he said the NIH is studying data on people who take an initial dose of one vaccine, such as Moderna, before getting a booster of another, such as Pfizer.

"The bottom line is there's a lot of substitution going on," Gottlieb said. "And that's why NIH undertook this study looking at the mixing and matching because some of that substitution is deliberate—people going out and getting a different vaccine than what they got. But a lot of it is inadvertent. In a big country, there are absolutely people who had Moderna who are getting Pfizer, and people who had Pfizer who are getting Moderna because they're not keeping track well."

Gottlieb said that should results of this study, which he believes are on the way soon, show that there are no adverse health effects associated with mixing and matching, it could provide another avenue for those at high risk for serious illness to receive a booster.

Still, Gottlieb doesn't think people should "expect to see a broad recommendation from either the FDA or CDC saying you can and should be using these vaccines interchangeably." He's also hopeful that this "weird period" in which many are awaiting the results of both the Moderna and Johnson & Johnson booster shots and the NIH study "won't last more than a couple of weeks."

Currently, only Pfizer has had a booster vaccine approved by the FDA and CDC.

An end to the Delta wave

Gottlieb also recently predicted that the latest Delta variant wave in the U.S. will have run its course in the country by Thanksgiving.

"This may be the last major wave of infection. I think by Thanksgiving you'll have seen this move its way through the country," Gottlieb told CNN. "The virus isn’t going away, but prevalence levels will decline to a level that feels more manageable.”

The Delta variant has led to a rise in COVID cases in recent months, particularly in the South, though Gottlieb also said other regions will see an uptick over the coming weeks. The CDC estimates the national proportion of cases attributed to the Delta variant to be greater than 98% for the week ending September 18, 2021.